1. Field of the Invention
The present invention relates to the field of data transmission between a global positioning satellite (GPS) receiver and a computer host device. More particularly, the present invention relates to a data transmission between the GPS receiver and computer host devices that provide various types of serial data ports. More particularly yet, the present invention relates to a method of and system for data transmission between the GPS receiver and a host device that provides a USB and/or a RS-232 data port.
2. Description of the Prior Art
Most personal computers (PCs) are equipped with one or more serial ports for connecting peripherals or accessory devices. The serial ports are typically RS-232 ports with a multi-pin connector, such as a DB 9-pin or DB 25-pin connector. Some computer host devices have a USB port in addition to the RS-232 port, and still other host devices, particularly very small devices, such as the personal digital assistant (PDA), provide only an RS-232 port for connecting peripheral devices or accessories. In the foreseeable future, PDAs may incorporate a suitable USB port. A USB signal is transmitted with a +5V signal for powering a peripheral device; an RS-232 signal is not, and a separate power source is required to power the peripheral device.
Nowadays, users of a data input device, and particularly, a GPS receiver, would like to be able to carry a small lightweight data input device with them into various environments and connect them with a number of different host devices, such as a portable PC or a data logger. The GPS receiver must be small, lightweight and, ideally, connectable and capable of interfacing with host devices that provide a USB signal and/or an RS-232 signal. In order to achieve this connectability with USB and RS-232 devices today, a USB cable is required to connect the device to a host computer with only a USB port, and an RS-232 data cable, or a USB/RS-232 cable adapter, plus a separate power cable and battery pack, is needed to connect the device to a host with only an RS-232 port. If the user also intends to connect the device to a portable PC that is operated in a motor vehicle and provides only an RS-232 port, than it may be desirable to connect the power cable to the 12V power source in the vehicle, rather than to a battery pack. In this case, a power cable with a plug for the cigarette lighter socket is needed.
A partial solution to at least the problem of connecting to various external power sources was disclosed in U.S. Pat. No. 6,007,372 (Wood; 1999), which is assigned to the assignee of the present application and the contents of which are incorporated herein by reference. Wood teaches the use of a GPS data/power cable system that includes a data/power cable that has a separate power cable and a separate data cable attached to a connector in a Y-configuration. In one alternative, the data cable connects to a conventional COM port on a PPC and the power cable plugs into a conventional cigarette lighter receptacle in an automobile. In a second alternative, the power cable plugs into a conventional power connector on the PPC that is provided for input/output peripherals, such as for a typical computer mouse or an extra keyboard.
The Wood cable system did not address the problem of incomparability between USB and RS-232 interfaces. Some GPS receivers are constructed to transceive RS-232 serial data, while others transceive USB serial data. Thus, the buyer of a GPS receiver that transceives USB serial data cannot connect to a host that provides only an RS-232 interface. Cable adapters are available, however, that allow an RS-232 device to interface with a USB host through an RS-232/USB cable and, potentially, an external power source, such as a battery pack or cigarette lighter power source. Nevertheless, a user who is relatively unsophisticated in the use of electronic devices may not initially grasp that he cannot connect his newly acquired USB GPS receiver to an RS-232 host at all, or, in the other case, that he cannot connect the RS-232 GPS receiver to a USB host without acquiring an additional adapter or a different cable. The user, when looking to acquiring a GPS receiver and to connecting it various computer hosts, needs to know what types of serial data ports the various computer hosts provide, and, possibly, the various types of external power sources that will be used, in order to obtain the proper cables and adapters. The fact that various host devices provide interfaces that may not be compatible with the device just purchased often results in confusion or irritation on the part of the user; the necessary acquisition of additional cables and/or adapters that are necessary to obtain the desired functionality adds to the expense as well as irritation of the user.
What is needed, therefore, is a system for transceiving data between a GPS receiver and a host device. What is further needed is such a system that simplifies setup steps and reduces confusion for the user. What is yet further needed is such a system that transceives RS-232 and/or USB signals. What is still yet further needed is such a system that enables simultanous transmission of RS-232 and USB signals.